Flowmeters



L. L. POHL FLOWMETERS Dec. 15, 1964 6 Sheets-Sheet 1 Filed OCT.. 25, 1960 l S A INVENTOR. lfhnv Louhs Pal-Il L. L. POHL FLOWMETERS Dec. 15, 1964 Filed om. 25, 1960 6 Sheets-Sheet 2 migas a/"mjws Paw @im ym@- i'new Dec. 15, 1964 L.. Pol-n. 3,161,043

FLOWMETERS Filed Oct. 25, 1960 6 Sheets-Sheet 5 IIO H6 L. L. POHL FLOWMETERS Dec. l5, 1964 6 Sheets-Sheet 5 gym Mz., ,Mm wm@ mdf Filed 001'.. 25. 1960 United States Patent O Lothar Louis liohl, Toronto, ntario, (lanada, assigner to Specialized Patents Sales and Developments Limited,

Islington, Gntaro, Canada, a corporation of Canada .Fitted @ft 25,1966 Se?, No- 64,966 Claims priority, application Canada, linne 26,1958,

lt) .iaims. (Cl; 731-229) This application is a continuation-impart of my application Serial No. 789,370, led January 27, 1959, now abandoned.

This invention relates to apparatus responsive V to the velocity and rate of flow of a fluid medium liowing across a surface, and `is particularly concerned with a ilowmeter for measuring the rate, and volume of the flow of a iiuid medium.

Existing instruments Vfor measuring the rate of flow of a fluid medium, are almost exclusively fiowmeters con- -cerned with measuring the rate of iiow of a fluid medium through a conduit, and these may be divided into two broad classes. s

The `first of these is that type in which the fluid medium is forced to undergo a constriction in its ow path, thereby causing an increase in the flow velocity, and hence a corresponding reduction in the static pressure. The pressure dierential existingbetween the free flow, and the constricted flow areas?, is then a measure of the ow velocity ,and by measuring this pressure differential by'suitable means, such as, for example, a manometer, the flow velocity an be measured. The most common ways of creating the constriction in the tflow path are by athroat in the conduit, i.e. a Venturi meter,`or alternativelyby introducing an orifice plate into the flow stream. This type of equipment is sensitive to variations in atmospheric pressure, temperature, etc., and also in general, the pressure differential that the measuring equipment is capable of accommodating is quite limited, so that the equipment may be only used with a prescribed type of fluid medium owing under certain specified conditions. This type of iiowmeter is frequently found in large installations where information on flow velocity is all that is required, `since it is difficult to translate the flow velocity, as given by the .pressure differential, into a conveniently calibrated rate of ilowrneter, and from this into a volume of flow. This is complicated by the use of conversion tables or by the use of auxiliary evaluating equipment.

In the second class of ftowmeter most commonly employed today, a rotating vane or propeller, which may take thev form of a helically formed rotor, is placed in vthe center of the flow path of the fluid medium with its axis of rotation parallel to the direction of How. As the fluid medium flows through the rotor it causes it to rotate, and the speed of rotation varies in sympathy with the variation in the iiow velocity, so that by suitable connection to thisrrotating member anV indication may be obtained of the rate of flow. This system has several obvious drawbacks, not the least of which is the impediment introduced into the free ilow path of the fluid medium by the presence of the rotating vanes and associated supporting members which must, of course, also project into the flow path. Impeding the flow in this manner causes the flow to become disturbed, particularly when the flow velocity exceeds a certain value, and also there is an appreciable energy loss in the kinetic energy of the iiuid medium. The mechanical inertia of the moving is rapidly increasing away from 3, l 5 l ,M8 atented Dec. l5., i964 parts in this system is a serious drawback since it means that the response of the system to changes in flow velocity is sluggish, and also that at low flow Velocity the accuracy of the system is very dubious since an appreciable How Velocity is required before the vanes even start to rotate. Another drawback is that at high velocities the accuracy is affected by the fact that the vanes must, by their very nature, be supported on a downstream thrust bearing and as the flow velocity varies the pressure exerted on this thrust bearing will vary in sympathy and so therefis introduced la variable factor which affects the accuracy of the system. To obtain the best results high precision work, profile milling, and balancing of the vanes is required Vand is v ery costly.

There is disclosed in the present invention apparatus yfor measuring the flow velocity of a fluid medium through a casing which has the Virtue Vthat little or no impediment is offered to the free ow of the medium and which has the additional benefits of simplicity of design and lowered manufacturing costs and coupled with the fact that the information regarding the flow velocity, and also the volume of flow, may beextracted in a Yrelatively simple manner with proven equipment which uses the minimum of mojving parts, none of which are disposed in the main flow stream, so that the mechanical inertia of the mechanical system is as low as possible and its accuracy is relatively unaffected by varying ow velocity.

A characteristic of the present invention is that, in all its different embodiments, it utilizes the property common to all fluid media when flowing over a surface, that there Qis' created at the point where the fluid medium comes in contact with the surface a boundary layer, caused by the fact that the fluid medium in actual physical contact with the surface sticks to this surface and so its velocity is zero, inwardly from the surface the velocity of the fluid increases until it becomes substantially constant. The layer ,or thickness or vdepth Yover which the fluid .velocity the surface is known as the boundary layer. l

The basis of the present invention is the utilization of the knowledge ythat when a fluid medium is flowing through a casing, a rotating member comprising a single plate which ,has an aerodynamically designed profile can be so positioned with `is axis of rotation transverse to the direction Yof flow of the fluid medium through the casing that .it `is possible 1.to cause three different .forces to act upon the rotating member as it rotates, each force producing a turning momentv tending to rotate the rotating rnern' ber in the same direction, and suicient inthe aggregate to sustain continuous rotation of the member at a speed proportional to the flow velocity of the fluid medium through .the casing. These three forces which may be best considered respectively as aerodynamic lift, dynamic, and static pressure forces, must of course represent an energy loss from the `flowing iluid medium but the loss is very much smaller `than that encountered in any other known form of dov/ meter and an extremely small impediment is offered to the passage of the fluid medium by the owmeter disclosed in this invention. Thus themanufacture of lthis new flowrneter is simplified at less cost.

When formed according to this invention a flowmeter -for determining the rate of flow of a uid medium ,corn-r prises a casing, Vmeans, defining a ow path/for said iiuid medium through said casing, means for increasingv the' defining at least one cavity in said portion of said flow path, a single rotating blade member having an aerodynamically designed prole mounted in said cavity for rotation about an axis transverse to the direction of flow of said fluid medium through said casing at said cavity, and also parallel to the mean plane of the iiow surface of said casing adjoining said cavity, and means associated with said rotating member having an output proportional to the speed of rotation of said member, said rotating member in its rotation having at least one position whereat one edge of said member projects into the main iow stream of said fluid medium through said casing and a second position whereat said single rotating blade member is contained substantially entirely within said cavity, whereby to cause said rotating member in rotating to experience successively aerodynamic lift, dynamic, and static pressure forces each tending to rotate said member and sufficient in the aggregate to sustain continuous rotation of said member.

The information concerning the angular rotational velocity of the rotating member may be extracted by conventional mechanical or electro-mechanical means or alternatively a novel electrical sensing unit disclosed in this invention may be used which permits the rotational information to be extracted in the form of electrical signals, which may then be processed in a variety of ways in order to present the flow velocity or the volume ofiiow information in whatever form is most appropriate for the particular use to which the invention is to be put.

The novel electrically-energised sensing unit of the present invention includes a reactance circuit element, such as a coil or a condenser, which is part of an oscillator positioned so that its reactive impedance varies in sympathy with the rotation of the rotatable member in the cavity whereby the generated electrical signals appear as modulation of a high frequency carrier in the output.

In connection with the use of the word constriction in the present specification, this word is employed-in the sense in which it means contraction followed by expansion in general back to the original pre-contracted level, and will be used in this specific manner throughout this specification, including the claims. g

A greater understanding of the basic inventive concept of the present invention, and of the manner in which it is employed in practice, will be gained from the study of the following description of certain flow theory associated with the invention, and of the various embodiments disclosed, when taken in conjunction with the accompanying drawings in which FIGS. 1, 2 and 3 show in cross-section the principal components of a preferred embodiment of a fiowmeter formed according to the present invention, the rotating member in each of the figures being shown in a different position where a different type of rotational force is being experienced by the member.

FIG. 1 shows the position of the rotating member when it is experiencing a static pressure rotational moment.

FIG. 2 shows it when it is experiencing an aerodynamic lift rotational moment; FIG. 2a showing the aerodynamic lift and drag forces and their resulting rotational moment.

FIG. 3 shows the member in the position where it is experiencing a dynamic pressure rotational moment.

FIG. 4 shows a side elevation in cross-section of a flowmeter formed as a preferred embodiment of the present invention;

FIG. 5 shows an end elevation of the iiowmeter of FIGURE 4 along the lines 5 5 of FIGURE 4;

FIG. 6 shows two different types of rotatable members which are preferably used, FIGURE 6a showing a fiat member, and 6h showing a twisted member;

FIGURE 7 illustrates in diagrammatic form how the sensing element is used to extract the rotational information of the rotating member of FIGURES 4 and 5;

FIG. 8 is the block diagram of an electronic circuit which may be suitably associated with the sensing element of FIGURE 7 to give the desired rate, and volume, of iiow information;

FIGURES 9a and 9b show the modulation envelopes at different rotational speeds for the modulated carrier of FIGURE 8, and

FIGURES 10a and 10b show the resultant output wave form from FIG. 9. FIGURE 10a showing the output wave form immediately after detection, and FIGURE 10b showing the output wave form after detection and clipplus;

FIGURE 11 shows an alternative conguration for the ensing element used in conjunction with the flowmcter of FIGURES 4 and 5. FIGURE 11a showing an end elevation of this sensing element, FIGURE 11b showing a side elevation of this sensing element and FIGURE 11C showing how the end of the rotating member may be modified to give a more desirable velocity rotation speed calibra tion;

FIGURE 12 shows an alternative construction for the fiowmeter shown in FIGURES 4 and 5. FIGURE 12a being a cross-section in elevation, and FIGURE 12b being a perspective view with a side plate removed;

FIGURE 13 shows yet another form of construction of a owmeter. FIGURE 13a showing a detail of the actual measuring sub-assembly. FIGURE 13b showing an end elevation in cross-section of the complete assembly, and FIGURE 13e showing a plan View of the assembled owmeter;

FIGURE 14 shows a comparison of the velocity diagram and associated physical layout of a tiowmeter of the type shown in FIGURES 4 and 5, with those for a owmeter having only one rotating member disposed on either side of the tiow path, and FIGURE 14b showing the asymmetrical arrangement and velocity diagram when only one rotating member is disposed adjacent the flow path;

FIGURE 15 shows the construction of a modified form of rotational member which is more suitable for particular types of flow measurement.

FIGURE 16 and FIGURE 17 shows a removable subassembly which houses the rotating member and its bearings and which may be removed without interrupting the fluid iiow for maintenance purposes.

FIGURE 16 showing the sub-assembly in cross-section transverse to the direction of flow,

FIGURE 17 showing the sub-assembly in cross-section parallel to the direction of iiow,

FIGURES l, 2, 2a and 3 are included to give an explanation of the manner in which the system works and show the principal components of the system with the rotating member in different positions of its rotational arc.

It will be seen that the system comprises a casing C, through which flows a fluid medium in the direction of the arrow, the tiow path of the medium normally being of circular bore, but here, for convenience, it may be considered as being of rectangular bore. A constriction, by which is meant a uniform contraction in the iiow path area followed by a uniform expansion in the flow path area, is brought about by means of the projection P which rises from one side of the casing C, its surface following the contours normally associated with the Venturi type of meter, this of course being the form which gives smoothest contraction and expansion.

Downstream of the point 4of maximum constriction a cavity R is formed in the projection P. The inner surface of the cavity is, for reasons given below, preferentially made cylindrical in form, except where the downstream edge merges with the ilow surface, the axis of the cylinder being transverse to the direction of iiow of the iiuid me-` dium past the cavity.

Positioned in the cavity R and having its axis of rotation coincident with that of the cylinder, when the cavity is so formed, is a single rotating blade member B. As shown here, the member has a generally aerodynamically designed profile. Opposed edges of the member B are close to, but maintain constant separation from, the inner surface of the cavity R as member B rotates.

Referring to FlG. l it will be seen that the rotating member B and cavity R are so dimensioned, and positioned, that the rotating member can lie in a position generally vparallel to the ow of the iluid medium past the cavity R with both tips adjacent the` inner iiow surface of the cavity R that is with the single rotating blade member contained entirely or substantially entirely within the cavity R. This being the case, the fluid medium on the underside of the member B is essentially a ciosed body and presents uniform pressure to the underside of the aerodynamically designed profile of member B. On the upper surface the increasing cross-sectional area of the low path causes a downstream increase in the static pres.- sure present upon the upper surface of the aerodynamically designed prolileof member B. This means that the advance or upstream edge A is subject to less static pressure than is the trailing or downstream edge T, and this disparity of pressure produces a rotational moment tending to rotate the member B in the direction shown.

In FIGURE 2 the static pressure force has rotated the member to the point where thevadvance edge A is clear of the projection P and is starting to penetrate the tlow stream. Here conditions are 'as shown in FIGURE 2a. The iuid medium flowing in the direction of the arrow meets the streamlined aerodynamically formed protile,

and creates on it, in the manner of other aerofoils, lift Y offset from the axis of rotation E 4towards the leading edge A of the member B. Both `the lift and drag forces, but principally the lift force, have components which lie in a direction perpendicular to the chord axis of the profile of member B, this being represented in FIGURE 2a by the vector F. This force is offset by a distance rF from the axis lof rotation E so that a tuining moment of FJ'F acts to rotate the member B.

In FIGURE 3 the member B has rotated to the point where the advance or upstream edge A has penetrated appreciably into the flow stream and is experiencing a dynamic `pressure due to the flowing medium (as exemplied by streamline S) which produces a tangential torque continuing the rotation of the member back to the posi- `tion shown in FIGURE l when advance A and trailing T, edges will have interchanged themselves in the 180 cycle. It will be obvious from the symmetry of the rotating member that the cycle will then repeat itself.

it willbe noted that in FGURES 2 and 3 the proximity .of the trailing edge T to the inner surface of the cavity R isolates the advance edge from any interfering iiow patterns which would occur if .such proximity with the inner dow surface was not maintained. Thus -t-he configuration. shown gives maximum benefits but it should be borney in mind that the cavity may have other less efficient forms without rendering the system unusable, so that the cylindrical inner flow surface for the cavity R should be regarded as the preferred, but not the essential, form of this surface.

Similarly though ,symmetry about its axis of rotation may be regarded as essential, there may in fact be proles for rotating member- B which are not so symmetrical. More will be said later of possible profile forms in connection with FIGURE 6. i

One preferred form of owmeter is shown in FIG- URES 4 and 5. The fiowmeter generally indicated by the reference numeral li, comprises an outer casing 17 'having a cylindrical bore through it, effectively forming a length of conduit, and which is capable -of connection at either end to any pipe through which the iiuid medium may be flowing. The diameter of this bore is D. From the intake region 2 the cross-sectional area of the flow path contracts to a central region 3 where the ow path is of reduced vertical dimension d. Downstream beyond this constricted area 3 the flow path again widens until it returns to the original conduit dimension D inthe outlet region 4. The contraction in the ow path is intro.- duced smoothly and continuously by the inlet portion 5 and the outlet or diffuser portion' expands the iiow path gradually and smoothly on the downstream side, the flow surfaces of these portions being of high finish to minimize disturbance. Sections 5 and 6 are integrated with the casing 1.7 either by being fabricated separately and then attached by suitable means such as brazing o r welding, or alternatively may be cast in one unit with the casing. As will be best seen from FIGURE 5, `these two portions, in this particular embodiment, are not annular as is the case with a venturi meter but have substantially flat inner surfaces forming chords of the circle defined by the bore of the casing 17 so that the constricted area 3 is very nearly rectangular in crosssection with straight upper and v lower edges and curved side edges.

The amount of constriction of the cross-sectional area of the flow path obviously governs the extent to which the velocity of the uid medium is increased and in a typical example the ratio 'of the cross-sectional area of the free ow path i.e. in the open conduit of diameter D, to the constricted area i.e. at the point where the vertical dimension of the flow path has been reduced to small d, was approximately 3:2, which caused a velocity increase in the ratio of' l.6 :1, as given by the equation derived from the fact that the quantity of iiow is constant, namely.

where A is the area of the bore of diameter D, va., is the mean velocity, Cc is the coefiicient of contraction, `and is given by the ratio of the calculated cross-sectional area of the flow path at the vena contracta, to the cross-sectional area ri of the flow path at the point of maximum constriction, a is the cross-sectional area at this point of maximum constriction, and vc is the meanvelocity ofthe fluid medium at a point of maximum constriction. T he angles of the tiat inner flow surfaces of the inlet'and outlet positions 5 and 6 subtend with the bore axis are critical since the constriction in the flow path of the iiuid medium should be accomplished smoothly and continuously withy out either excessive contraction or excessive expansion. The angle of the inlet portion S preferably lies in the range of l() to 20 degrees and the angle of the outlet portion 6 in the range of from 5 to 15 degrees. In a typical flowrneter the two angles were 14 degrees and 10 degrees respectively.

The inlet and outlet portions 5 and v6 are in line with one another, and the cross-sectional area of the tlow path at the downstreamedge of the inlet portion is V,made less than that at the upstream edge of the outlet portion, sothat between these two points the cross-sectional area of the flow path increases in a downstream direction.

These two portions are spaced apart in a downstream direction and the interruption `in their surfaces defines the limits of a central portion of the assembly, the outer edges of this central portion thus being contiguous to and merging smoothly with those of the inlet and outlet portions. At the point of maximum constriction there are located therefore upper and lower central portions, in which are diarnmetrically opposed cavities 7, which are designed for optimum performance in the manner described above, each cavity extending transversely tothe directon of flow for substantially the full width of the conduit. In each of these cavities is located an aerodynamically designed member S, which-may have various forms as described below.

The positioning of the rotating member in the cavity has been described above and is such that the longitudinal axis, about which the rotating member 8 rotates, and which will normally be the longitudinal axis of symmetry, is disposed transversely to the direction of flow of the fluid medium, and at the same time parallel to the plane of the boundary layer of the main flow moving across the cavity opening, the exact position of this plane is diiicult to define since it may be curved in certain applications where the downstream edge of the inlet portion is not flat across its entire width, and it is perhaps better to define the position of the axis as being parallel to the mean plane of the flow surface adjoining the cavity.

At either end of each rotating member 8 is a journal shaft 21 as is best seen in FIGURE 5. These shafts are journalled into bearings 22 and 23 respectively at either end of the rotating member which support this member 8 for rotation about the longitudinal axis. Bearing 22 mounts directly in the casing sealed off by seal 2d but bearing 23 is mounted in a bearing block which in turn screws into the casing. The member is first inserted through the bore which houses the block for bearing 23 until it engages the bearing surface of bearing 2l, when the block for bearing 23 is inserted and screwed into place. The bearing assembly is sealed off on either side by two side plates 25 which are held in position by screws 26.

For the average type of duty the rotating member S may most conveniently, and preferably, have the form shown in FIGURE 6a. However, other applications may produce variations in the profile of this rotatingfmember, and also may require variations in the profile placement along the axis of rotation. For example, it may be desirable in certain applications to use the modified form of construction shown in FIGURE 6b, where the chord axis of the rotating member shown in FIGURE 6a has been rotated slowly but continuously and unidirectionally throughout its length, producing a helical twist in the member. The advantage of this construction is that it tends to level out the rotational forces since one portion of the member will be undergoing dynamic or static pressure forces while another is experiencing aerodynamic lift and so on depending on the degree of twist. Thus a more uniform rotational moment can be produced but at the expense of some interaction between the forces along the length of the member, giving slightly increased energy losses.

Other profiles may be dictated by the type of fluid medium being measured, and also its velocity. Thus, for example, in very high speed measurements it may be preferable to use a rotating member whose profile is essentially a low diamond shape, and again an S-shaped profile may be preferable when it is desired to obtain most effect from the dynamic pressure forces.

The profile of the rotating member must therefore be determined for the specific application to which the flowmeter is to be put, but of course any given fiowmeter will cover a broad range of fluid mediums and iiow velocities. An example of this particularly is described below in connection with FIGURE which shows a rotating member structure designed for use in tlowmeters which must be sensitive to low flow velocities.

The structure as described thus far will on the passage of a fluid medium through the bore of the tlowmeter, cause the rotating member 8 to rotate at a speed proportional to the main flow velocity of the fluid medium, but to be useful it is necessary that the flowmeter also include some means which, in association with the rotating member will give an output proportional to the speed of rotation of the member. The mechanism used, whatever its nature, will obviously have to be mounted in such a manner that it can respond to the rotation of the rotatable member, and may be suitably housed in a housing integrated with the main casing of the ilowmeter in the manner depicted in FIGURES 4 and 5 for unit i3.

The simplest and most direct means known of extracting information as to the rotation speed of a shaft are, of course, mechanical, or alternatively electro-mechanical. Examples will be a tachometer or speedometer directly driven by the shaft used to indicate the rate of flow, with ft an auxiliary gear drive for giving the volume of flow, in much the fashion that the speedometer of a car is arranged, or an electric motor could be used with its rotor driven by the member shaft. A variety of ways readily suggest themselves but all have the disadvantage that they require mechanical connection to the rotating member increasing its inertia, and hence the speed of response of the system. Where this is of little practical consequence these means can be usefully employed, but for those situations where this factorbecomes critical a novel sensing unit has been devised as is shown in the cross-sectional View of the upper unit i3 of FIGURE 4.

This unit is inserted in an annular cylindrical housing 14 which may suitably be cast with the casing 17. Inside this housing there is positioned an inductance coil 10 with its longitudinal axis generally normal to the axis of the bore and also at right angles to the longitudinal axis of the rotating member 8. Axially inside this coil 1t) there is introduced an iron core 1l which acts as a tuning slug for the coil. The coil l0 is mounted on a bed of nonmagnetic material 12 which is let into the wall of the casing 17, non-magnetic material is used so that any electro-magnetic field created around the coil is not affected by the presence of this mounting 12 which thus serves as a membrane. The membrane 12 is in turn held in position by a sealing gasket plate I8 which also serves to keep the coil it) in place. Surrounding the coil and fixing plate i8, is a mounting of similar non-magnetic material 19, which in turn is fixed firmly in position by the retainer 9, on top of which is placed plate 2t) which includes an electrical connector le from which contact is made to the terminals of the coil lt). The whole assembly is kept in piace by the cap l5 which is securely attached to the housing I4.

The manner in which the coil and the member S cooperate is best understood by having reference to FIG- URE 7 where it will be seen that the lines of force F set up around the coil l@ are periodically broken by the member 3 as it rotates, for in one position shown, the member 8 lies substantially normal to these lines of force, and in the other position it is substantially parallel to them. Thus as the member rotates it cuts the lines of force F every half cycle of revolution thereby effectively varying the reactive impedance of the coil 10 every half revolution of the rotating member 8.

The lines of force F are set up around the coil by electrical energy which is fed to the coil 10 from a suitable outside source. This source is here a highfrequency 0scillator and the sensing coil 10 forms the inductive part of the high frequency oscillator tuning circuit. p

The manner in which this varying impedance is utilized may differ with the application to which the fiowmeter is to be put but a typical circuit is shown in block diagram form in FIGURE 8. The coil l0 is included as part of the winding of an oscillator coil for the oscillator 111 which will, in the absence of any rotation of the rotating member 8, therefore have a fixed frequency output. A second, constant-frequency, oscillator has a slightly different frequency from that of oscillator lil, so that, much in the manner of the oscillator coils of a superheterodyne receiver, in the absence of any rotation of the rotating member 8, the two frequencies of oscillator 111 and oscillator 110 are mixed together to provide a constant frequency output. This constant frequency output is fed through the intermediate, or LF., amplifier 112 to the detector 1li. From here the detected output is fed to the puise separator 114 which performs two functions. Firstly, the peak D.C. level of any input of the detector is ctermined and combined with a fixed D.C. potential from the densitometer llo, and is then fed to the rate of flowmeter IIS, and secondly any modulation peaks present in the output from the detector 113 are clipped and shaped and fed through the pulse counter 117 to the quantity or mass flow, meter M8.

The manner in which the circuit functions is as follows: when the member S starts to rotate it alters the reactive impedance of the coil I@ which is turned for optimum performance by means of the tuning slug 11. As this. impedance varies with every half revolution it effectively modulates the beat frequency emerging from the frequency converter stage of oscillator 111. Varying the speed of rotating member 8, in addition to varying the frequency of the modulation envelope, also aifects the percentage of modulation of the basic carrier frequency, since the `more rapidly the rotating member 3 cuts the lines of force F of coil the greater the variation in the impedance of the coil, so that an increase in the rotation speed of the rotating member is accompanied by an increase in the modulation frequency, and also in the percentage modulation of the carrier.

This is` shown in FIGURE 9, Where FIGURE 9a shows the resultant intermediate frequency modulated wave form for a low revolution number and FIGURE 9b shows that for a high revolution number.

After detection these two wave forms emerge as shown in FIGURE 10a. Both oscillate about the same mean D.C. level, Em, though at different frequencies and to different peak levels. To this mean DC. level Em, there has been added a constant D.C. potential Ed whose value is established by the densitometer 116, and which represents a variable D.C. component provided to compensate for diering densities of the fluid iiowing through the ilowmeter, so that the output of the electronic system will not be subject to error through variations in the density of `the fluid medium.

In the separator 114 the postive going output wave forms shown in FIGURE 10a are separated into two parts. The first portion fis passed through a smoothing filter which gives an output D.C. level proportional to the peak value of the rectified wave form, so that even through the two wave forms shown are oscillating about the same average D.C. level, Em, their peak levels, El and E2 respectively, are dierent due to the difference in the percentage modulation mentioned above. According- `ly the higher the revolution number the greater the' D C. potential emerging from the separator unit 114. The D.C. potential is fed tot the rate of ilowmeter 115, which -may suitably be a D.C. voltmeter appropriately calibrated in rate of flow units (gallons per hour, etc.) and the higher the revolution rate of the rotating member 8 the greater the D.C. level which will emerge from the separator unit 114 and accordingly the higher the rate of flow shown on meter 115.

Also in the pulse separator unit the other portion of `each-of the wave forms is D.C.` restored or clipped, for eX- ample by passing them through a capacitor and then a reetier, so that only the positive going half cycle of each wave form emerges in the manner shown in FIGURE 10b. Here the two wave forms have first been filtered so that they oscillate about the zero voltage level, and have had their negative-going half-cycles removed so that they now emerge as .a series of positive going pulses, with the number of pulses in any given period being dependent upon the frequencies f1 or f2, i.e. the revolution rate, so that the higher the speed of revolution of the rotating member 8, the greater the number of pulses emerging from the separator unit 114 and being fed to the pulse counter or integrator unit 117. In this unit the number of pulses in any given periodis added to give an `output from the integrator unit 117 proportional to the number of pulses lreceived in any given period of time. Since the number of pulses depends upon the rate of flow the total number of pulses in any given period of time is proportional to the total volume flowing in` that time, and so the indicator 118 will indicate the actual volume and mass of the fluid medium which has iiowed through the conduit in any given period and again this may suitably be a DC. voltmeter calibrated in gallons, etc. Alternatively each pulse can be used to actuate a step solenoid, which in .turn advances a Veeder-Root type counter.

From the foregoing it will be appreciated that this electrically energised sensing unit obtains its output proportional to `the speed of rotation of the rotating member, by having this member as it rotates vary the reactive impedance of a reactance circuit in sympathy with the rotation. To do this of course it is necessary that at least pant of the rotating member either be made of, or incorporate in its structure, material, such as a ferrous alloy, whose presence evokes this response.

The same circuit configuration as described above, may be used in conjunction with other means of developing the variable reactive impedance due to the rotation of the rotating member, one of which is shown in FIGURE 1l. Here a condenser unit has been positioned above the journal shaft 21 which fits into the bearing 22. Above this shaft is located a housing 27 fitted as before with an electrical connector 16; to the electrical connector are joined two leads which pass through a seal 29 into the area above the shaft 21. One of these leads goes to a capacitor plate 27 which may be a simple rectangle in form and the other to a brush contact 28 which makes contact with the shaft 21 and thence with the rotating member 8. There is thus effectively formed a condenser of known capacitance between the plate 29 and the rotating member S by means of the brush contact 28. It will be obvious that as the rotating member 8 rotates the capacitance present between the two leads connected to plate 27 and brush contact 28 will vary in sympathy with the rotation of the rotating member and will do' so twice evry revolution of the member. This varying capacitance creates a varying reactive impedance in the manner described above for the coil 10 and its output may be processed in. the same manner.

In order to give a more discrete and appreciable capacitance variation the end of the rotating member 8 may be modified in the manner shown in FIGURE llc by attaching a capacitive plate 30 to the end of the member 8, this plate being so shaped that the variation in capacitance present between the two terminal contacts` gives an output more suitable for processing in the electronic circuit.

In order to obtain the benets conferred by symmetry of flow, the flowmeter shown in FIGURES 4 yand 5 had two cavities, two rotating members and two sensing units diametrically opposed on either side of the iiow path. It should be obvious that only one system is necessary to give the rate of ow information and the manner in which the flowmeter behaviour is modified in this case is described later in connection with FIGURE 14, the second rotating member of the flowmeter of FIGURES 4 and 5 is far from being superfluous however, since it provides backup protection if one unit should fail and also it is a relatively simple matter to add an averaging circuit, which has as its output a reading equal to the mean value of the iiow velocity as indicated by each rotating member increasing the reliability of the system. Further by installing rotating members each with a different prole the measurement range and accuracy can be increased. r

The manner of constructing the ilowmeter can also be varied in various ways to improve the product and to cut down production, asesmbly, and maintenance costsone of which is shown in FIGURE 12. Here the owmeter 1 has been made in three parts, an inlet section which contains the inwardly curved inlet portions 5, a central section containing the rotating member 8 chambers .and the sensing units 13, and an outlet section containing the outwardly curved outlet or diffuser portion 6. This facilitates manufacture and assembly of the unit and also means that, should a part need replacing in the field', it is not necessary to replace the entire unit but merely the section which is defective, which will usually be the central section containing rotating member 8 and the sensing units 13. The manner in which the units are as.- sembled is shown in FIGURE 12b, which depicts the 't l. side plate 25 and its retaining screws 26 removed .in an exploded view.

Yet another type of construction is shown in FIGURE 13, here the flared inlet and outlet portions and 6, together with the rotating member S in their associated cavities 7, are formed as one unit mounted on a sealing pad 32 which in turn is mounted on a base plate `33. The sensing units are housed in a compartment 31 in the inlet portion S, as shown in FiGURE 13a. In use the complete assembly is inserted into the casing i7, in the manner shown in FIGURES 13b and 13C, and the flow stream at this point is therefore divided into two portions each of which flows past a different cavity.

`It should be noted that the velocity diagram with this configuration will vary somewhat from that for the flowmeter of FIGURES 4 and 5 where the two cavities were symmetrically disposed on either side of the conduit. The velocity diagram for that constriction is, as shown in FIG- URE 14a, i.e. a virtually flat top curved with some flow reversal at the two cavities. With the configuration shown in FIGURE 13, the velocity diagram will be modified in the manner shown in FIGURE 1417 where only one rotational system is depicted mounted opposite a fiat walled conduit 17. Here the velocity inwardly of the conduit liow surface increases up to the cavity in a generally uniform manner and then abruptly reverses as the velocity diagram shows. It will be obvious that the velocity reading indicated in these two cases will be diiierent even though the constriction in the tiow path be the same. This however, can be calculated and compensated for in the electronic circuitry described above, this being one of the inherent advantages of this type of unit in that, due to the absence of mechanical connection and the relative ease with which variations can be made, or corrections applied, to the output, various types of configurations for the different types of fiowmeter can be used with a minimum of adjustment.

In the flowmeters described so far the rotating member has been in the form of asingle unit. From the description accompanying FIG. l it will be recalled that in certain positions the rotating member may be subject to only static pressure forces, and this force considered alone, particularly at low fiow velocities, does not produce as substantial a rotational movement as do the aerodynamic and dynamic pressure forces. Thus if by chance the rotating member stops in the position shown in FIG. l, and the fiuid medium is then passed through the iiowmeter at low velocity, or alternatively if the fiowmcter is stopped and started frequently, as for example in a domestic gas or water meter, the slow starting response with the rotating member in this position is a disadvantage. It is tine that the response of the member to a given pressure diterential can be increased by the use of high precision bearings, light weight materials, etc., but this expense is not necessary.

The helically twisted rotating memberishown in FIG. 6b offers a solution to this problem, but a large amount of twist is normally necessary, between 45 and 90, and this considerably lowers the lift forces produced on the rotating member and also the effect of the dynamic forces, another by-product being the generation of a side force thrusting on one of the support bearings for the rotating member; the general result being a lowered overall efiiciency.

A form of rotating member construction which gives fast response but without the efficiency losses of the twisted member is shown in FIG. 15. It will be seen that the rotating member is now formed in two identical sections 81 and 82 lying along a common axis but with their chord axes at right angles to one another. Shaft 2i projecting from each end is used for mounting the member. Now

if one section should stop in the position where it will only experience static pressure when flow starts again, the other member section will be positioned so as to experience maximum dynamic pressure j reducing immediate response i2 on the rotational member. There is some reduction of lift force in this modified rotating member construction, and also there would be an aerodynamic interaction between the two sections, but this is prevented by the presence of the disc 4G interposed between the two sections 8l and 82 which prevents any such interaction.

As a practical form of construction the shaft 21 may be made of steel, the two sections 81, 82, of plastic material, and the disc 4) of alternate quadrants 41, 4Z, 43 and 44 (not visible) of similar metals welded together to produce different signal levels in the electronic sensing unit which extracts the information as to the rotating member velocity.

rIn use it is possible that the bearings for the rotating member will need replacement, or else this member itself will need attention. In this case it would be useful to be able to remove the member and bearing assembly without disturbing the fiow of the iiuid medium through the flowmeter, as the other rotating assembly could continue t0 supply flow velocity information. Such a subassembly is shown in FIGS. 16 and 17.

The inner flow surface of the cavity 7 is made in the form of a cylindrical steel or brass liner 51 provided with an appropriately contoured slot 55 communicating the cavity with the main ow stream, and also a non-metallic insert 56 which permits the member 8 in rotating to affect the sensing coil itl in the response unit 14. The rotating member 8 is positioned in this cylinder and supported on bearings 22 and 23 so that the liner 51 and its associated rotating member and bearings provide a neat subassembly.

This cylinder or liner 51 is positioned in a support block attached to the conduit 17 and is a tight t in this block, and also, of course, tits tightly against the inlet and outlet portions 5 and 6.

In normal use the sub-assembly is positioned in the blocl. The slot exposes the rotating member to the flow stream, and the end caps 52 (see hereon one end only in FIG. 16) seal the unit.

However, in case the assembly has to be removed, the steel cylinder or liner 51 is rotated by any suitable means, for example notches cut in one end, until the solid portion of the liner covers the entrance to the cavity 7, thus sealing the sub-assembly from the fiuid medium.

The end caps may then be removed and the subassembly extracted. But of course the gap made by the removal of the sub-assembly must be closed, and this is done by means of a tool rod 53 in the Iform of a brass or similar cylinder of identical diameter to the liner 51. This tool rod 53 may convieniently have a threaded projection S4 at one end which engages a threaded bore on the inner surface of liner 51 (and thus when tightened will provide a means of rotating the liner 51), so that no interruption in the seal against the fluid medium is made as the rod is tapped to push out the sub-assembly. Once the sub-assembly emerges on the far side unscrewed from the rod and sent away for attention, the rod remaining in place until the sub-assembly is replaced.

I claim:

1. A iiowmeter for determining the rate of iiow of a fiuid medium, comprising a casing, means defining a flow path for said iiuid medium through said casing, means for constricting the cross-sectional area of said flow path in a downstream direction to a point of maximum constriction, means for increasing theV cross-sectional area of said fiow path in a downstream direction from said point of maximum constriction, means defining a cavity in the flow surface of said cross-sectional area increasing means adjacent to but downstream from said point of maximum constriction of said flow path, a single rotating blade member having a profile of aerodynamic design mounted in said cavity for rotation about an axis transverse to the direction of flow of said fluid medium through said casing at said cavity, and also parallel to the mean plane of the flow surface of said casing adjoining said cavity, and means associated with said member having an output proportional to the speed of rotation of said member, said member in its rotation having one position whereat one edge of said member projects into the main flow stream of said iiuid medium through said casing and another position whereat said rotating mem-v ber is contained substantially entirely within said cavity, whereby to cause said member when said iiuid medium flows through said flow path to experience successively aerodynamic lift, dynamic, and static pressure forces each tending to rotate said member and sufiicient in the aggregate to sustain continuous rotation of said member.

2. A iowrneter for determining the rate of-fiow of a fluid medium comprising a casing essentially defining a length of conduit of varying cross-section, said casing comprising an inlet portion wherein the iiow surface of said casing converges smoothly and continuously in a downstream direction whereby to decrease the cross-seo tional area of the flow path of said fluid medium, an

`outlet portion downstream of said inlet portion wherein the ow surface of said casing diverges smoothly and contiguously in a downstream direction whereby to increase the cross-sectional area of the ow path of said fluid medium, a central portion connecting said inlet and outlet portions and having the outer edges of its ow sur-face contiguous with those of said connected portions, means defining a cavity in the ow surface of said central portion, said central portion being so formed that the cross-sectional area of said tio-w path is least at a position adjacent to but upstream from said cavity, a single rotating blade member having a profile o-f aerodynamic design mounted `for rotation in said cavity, the axis of rotation of said member being positioned transversely to the direction of flow of said fluid medium across said cavity and parallel to the mean plane of the iiow surface of said central portion adjoining said cavity, and means associated with said member having an output proportional to the speed of rotation of said member, said member 'being so dimensioned and positioned that at one position at least an edge portion of said member in rotating penetrates the main iiow stream ot said uid medium over said cavity and at another position said rotating member is contained substantially entirely within said cavity, whereby to cause said rnember when saidvluid medium ows through said tiow path to experience successively primarily aerodynamic lift, dynamic, and static pressure forces each tending to rotate the member andl sutiicient in the aggregate to sustain continuous rotation of said member.

3. A flowmeter according to claim 2 wherein said associated means comprise an electrically energized sensing unit, which is part of a tuned oscillating circuit, including at least one reactance circuit element disposed so that its reactive impedance varies in sympathy with the rotation of said member; said output being an amplitude or frequency modulation of the high frequency carrier of the tuned oscillator being presented across a set of terminals connected-to said circuit element.

4. A flowmeter according to claim 2 wherein said associated means comprises an electrically energized sensing unit including an inductance coil, adapted to be supplied with electrical high frequency energy from a suitable oscillator, positioned adjacent said rotating member, whereby said members edges in rotating cut the electromagnetic lines of force surrounding said coil due to the electrical energy flowing therethrough.

5. A flowmeter according to claim 2 wherein said means associated with said rotating member comprises an electrically energized sensing unit, including a condenser adapted to be part of a tuned oscillating circuit and supplied with high frequency energy from this oscillator, one plate of said condenser being in electrical contact with said rotating member and the other plate being isolated from said rotating member but positoned adjacent to it whereby rotation of said rotating member is effective to vary the capacitance of said condenser and hence the capacitive reactance present at the terminals of said condenser and causing an amplitude or frequency modulation of the oscillator high frequency carrier.

6. A owmeter according to claim 1 wherein said singie rotating blade member is so dimensioned and posiioned as to cause said member in rotating to project into the main iiow stream of said iiuid medium passing said cavity a distance equal to from about 20% to about 30% of the diameter of the cylinder swept by said member in rotating.

7. A flowmeter for determining the rate of flow of a diuid medium in a conduit comprising a casing having a generally cylindrical bore therethrough; means at either end of said casing for connecting said casing to said conduit; an inlet portion integrated with said casing, effective to contract the cross-sectional area of the `flow path of said fluid medium in said bore in a downstream direction, said inlet portion having a substantially flat flow surface whereby said inlet portions flat ow surface essentially forms chords of the circle defined by said bore and said contraction increases smoothly and continuously throughout the length of said inlet portion; a flared outlet portion colinear with and downstream of said inlet portion and integrated with said casing, downstream of said inlet portion, said outlet portion being etfective to expand the cross-sectional area of said iiow path in a downstream direction and having a substantially at flow surface whereby said outlet portions fiat liow surface essentialy forms chords of the circle defined by said bore and said expansion increases smoothly and continuously throughout the length of said outlet portion, the cross-sectional area of said flow path at the upstream end o-f said outlet portion beingnot less than that at the downstream end of said inlet portion; a central portion located between said inlet and outlet portions and colinear therewith, the flow surfaces` of said central portion at the upstream and downstream edges thereof being contiguous with the downstream and upstream edges of said associated inlet and outlet portions respectively; means dening a cylindrical cavity in the How surface of said central portion, the longitudinal axis of said cavity being transverse to the direction of iiow of said fluid medium and substantially parallel to the downstream edge of said flat flow surface of said inlet portion, and the walls of said cavity being interrupted over a portion of their circumference whereby to provide communicaiton between said cavity and said bore irnmediately adjacent said cavity; an elongated single rotating blade member having a profile of aerodynamic design mounted for rotation in said cavity about a longitudinal axis, said axis being coincident with that of said cavity and said member in its rotation having, one positionr whereat one edge of said member projects through the interruption in the walls of said cavity and another position whereat said rotating member is contained substantially entirely within said cavity; and means associated l with said rotating member having an output proportional to the speed of rotation of said member.

8. A iiowmeter according to` claim 7 wherein said at ow surface of said flared outlet portion subtends an angle of from 5 to l5 degrees with the axis of said bore, and the said flat flow surface of said flared inlet portion subtends an angle lying in the range of from l0 to 20 degrees with saidv axis of said bore.

9. A iiowmeter according to claim 1, wherein a cylindrical liner is fitted snugly within said cavity, said liner being axially displaceable from said cavity and being provided with a slot providing communication between its interior and said how path, said rotating member being rotatably mounted inside said liner and removable therewith, said liner being rotatable so that its interior may be isolated from said ow path, said liner being further provided with means for attaching thereto a cylindrical rod of vdiameter identical with that of said liner whereby said liner may be axially displaced and replaced by said rod.

l0. A llowmeter according to claim 1 wherein said single rotating blade member is so dimensioned and positioned as to cause said member in rotating to project into the main flow stream of said uid medium passing said cavity a distance equal to substantially about 50% of the diameter of the cylinder swept by said member 'in rotating.

l References Cited by the Examiner FOREIGN PATENTS 2/ 48 Great Britain. 6/54 France. 

1. A FLOWMETER FOR DETERMINING THE RATE OF FLOW OF A FLUID MEDIUM, COMPRISING A CASING, MEANS DEFINING A FLOW PATH FOR SAID FLUID MEDIUM THROUGH SAID CASING, MEANS FOR CONSTRICTING THE CROSS-SECTIONAL AREA OF SAID FLOW PATH IN A DOWNSTREAM DIRECTION TO A POINT OF MAXIMUM CONSTRICTION, MEANS FOR INCREASING THE CROSS-SECTIONAL AREA OF SAID FLOW PATH IN A DOWNSTREAM DIRECTION FROM SAID POINT OF MAXIMUM CONSTRICTION, MEANS DEFINING A CAVITY IN THE FLOW SURFACE OF SAID CROSS-SECTIONAL AREA INCREASING MEANS ADJACENT TO BUT DOWNSTREAM FROM SAID POINT OF MAXIMUM CONSTRICTION OF SAID FLOW PATH, A SINGLE ROTATING BLADE MEMBER HAVING A PROFILE OF AERODYNAMIC DESIGN MOUNTED IN SAID CAVITY FOR ROTATION ABOUT AN AXIS TRANSVERSE TO THE DIRECTION OF FLOW OF SAID FLUID MEDIUM THROUGH SAID CASING AT SAID CAVITY, AND ALSO PARALLEL TO THE MEAN PLANE OF THE FLOW SURFACE OF SAID CASING ADJOINING SAID CAVITY, AND MEANS ASSOCIATED WITH SAID MEMBER HAVING AN OUTPUT PROPORTIONAL TO THE SPEED OF ROTATION OF SAID MEMBER, SAID MEMBER IN ITS ROTATION HAVING ONE POSITION WHEREAT ONE EDGE OF SAID MEMBER PROJECTS INTO THE MAIN FLOW STREAM OF SAID FLUID MEDIUM THROUGH SAID CASING AND ANOTHER POSITION WHEREAT SAID ROTATING MEMBER IS CONTAINED SUBSTANTIALLY ENTIRELY WITHIN SAID CAVITY, WHEREBY TO CAUSE SAID MEMBER WHEN SAID FLUID MEDIUM FLOWS THROUGH SAID FLOW PATH TO EXPERIENCE SUCCESSIVELY AERODYNAMIC LIFT, DYNAMIC, AND STATIC PRESSURE FORCES EACH TENDING TO ROTATE SAID MEMBER AND SUFFICIENT IN THE AGGREGATE TO SUSTAIN CONTINUOUS ROTATION OF SAID MEMBER. 